I contributed the craft for the two-year-old class at the kids' preschool for their Halloween party. I shamelessly stole the idea from an activity they did at the French school before we left.
First, you get some tupperware containers or re-purposed food containers with lids. Trace around the bottom onto construction paper, cut out the shape, and fix the construction paper to the bottom of the container with tape. (Amelie & James helped me with this, but I just did it in advance for the party.)
Next, have the kids make a spiderweb shape onto the paper (just squirt glue out all over it). Dump in some glitter, put the lids back on, and have them shake it up.
Voila! Spiderwebs. I had Amelie and James do it just to see how it would turn out. They stuck their webs onto more construction paper and then drew spiders around them. (Well, Amelie drew spiders and wrote her name on hers; James said "Draw name!" so I wrote his name. He scribbled for a while, then he wanted me to draw some spiders on his, too.)